With MSS and MBT questions you accept everything said in the stimulus as true. It's usually not an argument, just a set of information about a topic. When it is an argument, it doesn't matter for these question types, you just treat all the statements as true. However, that doesn't mean you treat claims as facts. If a sentence says "Historians believe early typewriters would jam frequently if adjacent keys were struck in quick succession", you don't treat the claim as fact, you just accept as true that historians have that opinion, but when a sentence states something as fact, such as "early typewriters would jam frequently if adjacent keys were struck in quick succession", you treat it as established fact because they tell you it is true.
With arguments for assumption family questions (weaken, strengthen, flawed method of reasoning, sufficient assumption, necessary assumption, parallel flaw, useful to evaluate the argument), you accept the premises of the argument as true, but not the conclusion. Your job is to evaluate why the conclusion is not logically proven by the premises and reasoning used to arrive at the conclusion, meaning, why the conclusion could be false even if all the evidence is true. Your analysis should be focused on figuring out the assumption(s) the argument relies on since the correct answer for all of these question types will relate to the unwarranted/flawed assumption(s) of the argument in a certain way depending on specific question type. If a causal statement in an argument is presented in the conclusion, of course you are supposed to be skeptical of it since your job is to evaluate why the argument fails to logically establish causation. However, if a cause and effect relationship is presented in a premise and stated to be true rather than presented as an opinion/claim/theory, then you must accept it as being a valid established cause and effect relationship.
It's only conclusions and assumptions that you treat skeptically and critically, you are required to treat all things presented as premises as true on the LSAT even when just stated without support. If a premise of an argument states that X causes Y, you accept it. If the conclusion states it, then you treat it critically as a logically flawed conclusion for assumption family question types.
Regarding the typewriter question and assumptions: The assumption you mentioned having to make for (E) in terms of computer keyboards not potentially having the same jamming issues as early typewriters is not an assumption you must make if you don't make a false assumption/misinterpret the subject matter.
The main reason people have trouble with this question and think (E) isn't well supported is because they misunderstand/make a false assumption about the subject matter of the stimulus, namely what a typewriter is, and think about the wrong things in terms of jamming issues and fail to recognize the significant difference between a typewriter and a computer keyboard. Typewriters mechanically/physically print/type out the letters onto a piece of paper as they are typed on the keys, typing on computer keyboards doesn't do that unless you specially configure something together with a printer. Computer keyboards are just an electronic input device, typing on them doesn't necessarily make a device/physical mechanism do something else that has a limited speed which could be outpaced by fast typing.
Many people mistakenly think that 'early typewriters' refers to machines such as:
--ImageRemoved--
or
Those are NOT typewriters, they are old computers/word processors! The keyboards on them are computer keyboards, not typewriters!
Based on that false assumption people then falsely assume the jamming issues the stimulus mentions is about two adjacent keys getting stuck/wedged together when pressed down at the same time due to big fat/wide clunky keys like can happen on some older computer keyboards with fat keys that are close together. Most people have at some point in life experienced this type of 'jamming' issue with some older or crappy computer keyboards where adjacent keys get stuck together when pressed down together and assume that is what the stimulus is talking about, crappy older keyboards with sticky keys due to the state of keyboard manufacturing technology at the time with bad design, crappy cheap plastic or whatever reason that made the keys crappy/stick-jam easily.
However, that is not what the stimulus is talking about! It's not about the actual keys getting jammed together (although that did happen with some typewriters) like people usually think, its about the printing mechanisms of typewriters getting jammed when people type letters faster than the machine can print them out.
Since it's an easy common sense from life experience assumption to make about keyboards and adjacent keys jamming when pressed together but is not actually what the stimulus is talking about, the LSAC writers used carefully selected wording to clearly establish that the jamming issue being discussed is not about adjacent keys getting stuck down together when pressed together due to being adjacent on the keyboard and getting pushed/smushed together and stuck down when pressed down at the same time and also that it is not about keys getting jammed due to crappy keyboard parts, cheap materials, bad construction/manufacturing, that makes them stick, jam, not pop back up fast enough or something.
"...because early typewriters would jam If adjacent keys were struck
in quick succession" The phrase 'quick succession' tells us they aren't talking about the problem of pressing two adjacent keys down at the same time since succession means one AFTER another, but instead are talking about how rapidly keys are pressed in a row. Notice that it doesn't say the keys would jam, it says the typewriter would jam. Combine that with the premise that QWERTY was designed to limit typing speed, meaning how fast characters are typed in succession, and it's established that the jamming issue is about and caused by inputting too much information too fast, not about keys getting stuck down due to poor quality sticky prone keys/keyboard and/or pressing two adjacent keys down together. It's not about the keys themselves getting jammed, it's about the typewriter machine getting jammed when it gets input faster than it can process.
It makes me feel old and makes me sad that I have to explain this and use pictures since it really hasn't been that long in history since typewriters went out of common use.
People that have trouble with this question usually misinterpret the meaning of 'typewriter' and falsely assume the word applies more broadly than it does and think it means old computers and word processor machines. It doesn't.
By early typewriters, this is an example of what the question is talking about:
A typewriter is actually what the word describes --a type writer. It is a machine that actually writes out each letter you type as you type, hence the name! When you press a key the machine physically prints the letter onto the paper in the machine, which is a mechanical/physical task. The jamming issue from typing too fast was because the writing/printing mechanism couldn't go very fast and could only print a small number of letters per second. If you typed really fast the machine couldn't keep up and print the letters as fast as they were typed in and that caused the physical printing mechanisms to jam due to overload. The stimulus spells this out fairly explicitly, the only part not explicitly spelled out in the text is the printing out the characters part, but speed of input is clearly presented as the problem, and the device is explicitly described as something that writes out the type --typewriter.
There is no physical printing/writing directly happening from each keystroke on a computer keyboard since you're just entering data electronically into the memory of a computer, hence no physical jamming of the mechanism will happen from flooding it with too many letters really fast, it's a computer with a microprocessor so its fast enough to keep up with a fast typist and be able to accept the input quickly without 'jamming'. This is all common sense stuff about computers. The keyboard is used to electronically input information into the computer for it to process and do various stuff with, not just to type a letter directly onto a piece of paper. LSAC expects you to have common sense understanding of everyday things people in in todays world have real life experiences with, which certainly includes computers. You are not only allowed to, you are expected to use basic common sense when reasoning about common real world topics/things college age people have been or are expected to have been exposed to and know basic things about through basic life experience and/or basic general education. Certain vocabulary is included, LSAC expects test takers to have a vocabulary of at least the level of an average college level student. Typewriter is not a specialized item that requires specialized education or unique life experience to have been exposed to, it's a word college students are expected to understand.
The crux of the support for the answer is understanding the basic definition of typewriter and significant difference between the function of a computer keyboard and the function of a typewriter, all of which are considered to be common sense topics. Typewriters physically print letters one by one onto paper as the letters are typed on the keys, computer keyboards don't do that and have no analogous physical process that happens with each keystroke that could take more time to do than it takes to type in each letter if you type fast.
So, instead of you having to assume that computer keyboards don't have the potential jamming issues early typewriters had, you are actually supposed to KNOW they don't based on understanding what a typewriter actually is compared to what a computer keyboard is! This is considered to be common historical knowledge that average college students have been taught/exposed to/and are expected to know unless they were raised by a pack of wolves.
If you simply recognize that the stimulus is historical (notice who presents the information, a Historian!) and is talking about old school mechanical typewriters from before the computer age, answer choice (E) should be pretty obvious since it's very strongly supported. Typing speed had to be limited on early typewriters because they couldn't physically print out letters as fast as some people could type and computer keyboards have no such speed limiting problem with accepting input since everything you type isn't supposed to be instantly printed as you type, and even if you want your computer to do that, printers are plenty fast to print way faster than you can type in our modern times.
Even if you've never seen a real typewriter before and have no real world familiarity with them, LSAC made sure to explicitly state the important details and clearly describe everything needed to piece everything together to make the inference presented in (E).
The dictionary definition of typewriter is clear and is a word LSAC expects college level people to know. People that have trouble accepting (E) usually fail to recognize that typewriter necessarily means the device physically prints the letters typed one by one onto paper as the keys are pressed and falsely think the word could refer to old school computers and word processors which do not print out letters as they are typed but instead store the information in the computer to print when you want. The key aspect is to at least recognize that typewriter necessarily means the machine directly writes out the letters you type instead of just inputting them into memory like a computer. This important part of the definition is conveniently explicit in the word itself with 'writer' so you can easily derive proper meaning from the descriptive name itself.
type·writ·er
1. an electric, electronic, or manual machine with keys for producing printlike characters one at a time on paper inserted around a roller.
In short, the trouble many people have with this question is because they make a false assumption about what the word typewriter actually means and/or fail to think about basic history and use common sense to properly interpret the topic of the stimulus. Typewriter is described as a distinct/different thing than a computer keyboard but many people mistakenly think early typewriter in this question just refers to really old computers, basic computers and/or word processor machines from the past even though those things are actually computers with keyboards not typewriters.
It's actually a pretty easy question if you don't forget that typewriters existed long before computers and don't misinterpret what 'early typewriters' is referring to in historical context.